diff --git a/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/blockchair/BlockchairApiSyncer.kt b/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/blockchair/BlockchairApiSyncer.kt
index 5dfeb528..ac159978 100644
--- a/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/blockchair/BlockchairApiSyncer.kt
+++ b/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/blockchair/BlockchairApiSyncer.kt
@@ -38,6 +38,7 @@ class BlockchairApiSyncer(
     override fun sync() {
         scanSingle()
             .subscribeOn(Schedulers.io())
+            .observeOn(Schedulers.io())
             .subscribe({}, {
                 handleError(it)
             }).let {
@@ -48,6 +49,7 @@ class BlockchairApiSyncer(
     override fun syncLastBlock() {
         syncLastBlockSingle()
             .subscribeOn(Schedulers.io())
+            .observeOn(Schedulers.io())
             .subscribe({}, {
                 handleError(it)
             }).let {
diff --git a/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/legacy/ApiSyncer.kt b/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/legacy/ApiSyncer.kt
index 8b098a2d..31976dd1 100644
--- a/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/legacy/ApiSyncer.kt
+++ b/bitcoincore/src/main/kotlin/io/horizontalsystems/bitcoincore/apisync/legacy/ApiSyncer.kt
@@ -34,6 +34,7 @@ class ApiSyncer(
     override fun sync() {
         val disposable = blockHashDiscovery.discoverBlockHashes()
             .subscribeOn(Schedulers.io())
+            .observeOn(Schedulers.io())
             .subscribe(
                 { (publicKeys, blockHashes) ->
                     val sortedUniqueBlockHashes = blockHashes.distinctBy { it.height }.sortedBy { it.height }